D-dimer inhibits platelet activation by collagen and fibrin in washed platelets. Platelets (500 × 10⁹/L) in the presence of D-dimer (30 μg/mL) were stimulated with collagen (Ai-ii) or CRP, PAR1-peptide, or fibrin (Bi-ii). Aggregation and secretion were monitored by lumiaggregometry (Chrono-Log). The figures show representative aggregation traces with histograms summarizing 3 independent experiments. The results are shown as mean ± standard deviation. *P < .05, **P < .01, ***P < .001.